1. Field of Invention
This invention pertains generally to wastewater treatment and, more particularly, to an anaerobic wastewater treatment system and process which utilize foreign substances in the influent stream.
2. Related Art
Large quantities of fecal matter can cling to foreign materials such as rags, condoms, diapers, unprocessed garbage, whole fruits and vegetables from canneries, sand, fist-sized rocks and lumber that come floating, tumbling and sliding into the headworks of wastewater treatment plants. Such materials must be removed from the influent stream to prevent them from clogging up the system or bogging down the treatment process. The fecal matter stays with the materials when they are removed, and with the pathogens and possible viruses in the fecal matter, it presents a serious health hazard to the people who are involved in the removal, transportation and disposal of the materials.
In larger cities where sewage travels several miles to treatment facilities or where collection systems are such that flow rates are slow, bacterial growth can be deeply colonized into every crack and crevice in the materials, and rags and other porous materials are often densely packed with fecal matter that is well colonized with bacteria and quite putrid. This fecal matter presents a large quantity of potential energy.
The foreign materials are removed by a wide variety of means and commonly transported to the local garbage dump, landfill, or incinerator. A plant that processes 10 million gallons per day can, for example, accumulate several cubic yards of such material every day. In addition to the health hazard, the removal, transportation, placement or spreading of the foreign materials consumes large amounts of energy and accounts for a large percentage of total plant operating costs. Moreover, the open aerobic digestion of the fecal material produces gasses that contribute to the greenhouse effect.